Conventionally, a device described in Patent Document 1, for example, is known as a vehicle seat reclining device. As shown in FIG. 26, a vehicle seat reclining device described in this document includes a lock mechanism 200. The lock mechanism 200 includes a first member 201 fixed to a seat cushion component, a second member 202 fixed to a seat back component and rotationally supported by the first member 201, a plurality of pawls 203, and a cam 204. The pawls 203 are guided by corresponding guide grooves 201a, which are located in the first member 201, to move in the radial direction. Each of the pawls 203 has outer teeth 203a, which are selectively meshed with and separated from inner teeth 202a, which are arranged in the second member 202. The cam 204 is rotationally provided in the first member 201. When the cam 204 is rotated in a certain direction and thus switched to a state of unlocking operation, the cam 204 retracts the pawls 203 radially inward to separate the outer teeth 203a from the inner teeth 202a. When the cam 204 is rotated in the opposite direction and thus switched to a state of locking operation, the cam 204 presses the pawls 203 radially outward to mesh the outer teeth 203a with the inner teeth 202a. The cam 204 is urged in the direction corresponding to the locking operation by an urging member (not shown) and rotated in the direction corresponding to the locking operation against the urging force of the urging member when a manipulating member (not shown) is switched to a state of unlocking manipulation.
A circular accommodating recess 202b, which is coaxial with the inner teeth 202a, is located in the second member 202. An annular memory ring 205, which has a discontinuous section, is rotationally arranged in the accommodating recess 202b in a contracted state. Pawl engaging projections 203b are provided in an adjacent pair of the pawls 203. The discontinuous section of the memory ring 205 is located between the pawl engaging projections 203b. The memory ring 205 has a pair of engagement portions 205a, 205b, which are arranged at positions adjacent to and between the pawl engaging projections 203b. The pawl engaging projections 203b are selectively engaged with and disengaged from the corresponding engagement portions 205a, 205b as the pawls 203 move radially.
When in a state of a first unlocking manipulation as an unlocking manipulation, the memory ring 205 is partially engaged in the radial direction with the pawl engaging projections 203b of the pawls 203, which are retracted radially inward, by means of the engagement portions 205a, 205b. The term “partial engagement (or engagement) in the radial direction” herein refers to a state in which the pawl engaging projections 203b of the pawls 203 are partially (or entirely) overlapped with the corresponding engagement portions 205a, 205b in the radial direction and thus interfere with the engagement portions 205a, 205b in the circumferential direction. This allows the memory ring 205 to rotate integrally with the first member 201 and relative to the second member 202.
In contrast, when in a state of a second unlocking manipulation as an unlocking manipulation, the engagement portion 205b of the memory ring 205 is disengaged in the radial direction from the pawl engaging projection 203b of the pawl 203, which is one of the pawls 203 that is retracted radially inward. This allows the memory ring 205 to rotate integrally with the second member 202 through friction engagement between the memory ring 205 and the second member 202 caused by elastic deformation of the memory ring 205 when, for example, the seat back is inclined forward.
At this time, the pawl engaging projection 203b of the corresponding pawl 203 is moved onto the engagement portion 205b to prohibit the outer teeth 203a of the pawls 203 from being meshed with the inner teeth 202a. That is, in the state of the second unlocking manipulation, the seat back, which is permitted to incline relative to the seat cushion, is inclined forward while being maintained in the state in which the seat back is permitted to incline relative to the seat back.
Then, the engagement portion 205b passes the pawl engaging projection 203b of the pawl 203, or, in other words, returns to the original angular position of the second unlocking manipulation (hereinafter, referred to as the “memory position”). This enables restriction of inclination of the seat back, which has been in the state permitted to incline. That is, by canceling forward inclination and returning the seat back, which has been inclined forward in the state of the second unlocking manipulation, to the memory position, inclination of the seat back becomes restricted.
A substantially arcuate engaging projection 202c projects radially inward from the second member 202. That is, as illustrated in FIG. 27, a circular recess 202d, which is coaxial with the inner teeth 202a and arranged radially inward from the inner teeth 202a, is located in the second member 202. The recess 202d is arranged such that at least a portion of the recess 202d is overlapped with the corresponding pawl engaging projection 203b at a position in the axial direction.
The engaging projection 202c projects from the inner circumferential surface of the recess 202d. As shown in FIG. 26, the engaging projection 202c is arranged such that the engaging projection 202c can be engaged in the radial direction with the pawl engaging projections 203b. When in the state of the first unlocking manipulation, the engaging projection 202c is partially engaged in the radial direction with the pawl engaging projection 203b of the corresponding pawl 203, which is retracted radially inward. The term “partial engagement (or engagement) in the radial direction” herein refers to a state in which the pawl engaging projection 203b of the pawl 203 is partially (or entirely) overlapped with the engaging projection 202c in the radial direction and thus interferes with the engaging projection 202c in a circumferential direction. This limits relative rotation of the first member 201 and the second member 202 to a predetermined relative rotation range at the end of which the engaging projection 202c contacts the corresponding pawl engaging projection 203b. Inclination of the seat back is thus limited to a predetermined angular range corresponding to the rotation range.
In the state of the second unlocking manipulation, the engaging projection 202c is disengaged in the radial direction from the pawl engaging projection 203b of the corresponding pawl 203, which is retracted radially inward. As a result, in the state of the second unlocking manipulation, the seal back can be inclined forward beyond the predetermined angular range.